Hi,
I just read this article on bullying, it's very good:
thebaffler.com/salvos/bullys-pulpit
I especially like this line:
"Studies also show that in general, if one or two onlookers object, then bullies back off."
This matches my experience, I once so a co-worker being bullied by his boss, all I did was stand up and look straight at his boss and he backed down immediately. I think children should be taught to spot bullies and intervene safely.